Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, turbomachines such as gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine includes an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section increases the pressure of the working fluid and supplies a compressed working fluid to the combustion section. The combustion section mixes fuel with the compressed working fluid and ignites the mixture to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity.
The combustion section may include multiple combustors annularly arranged between the compressor section and the turbine section, and various parameters influence the design and operation of the combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustor. However, higher combustion gas temperatures also promote flame holding conditions in which the combustion flame migrates towards the fuel being supplied by nozzles, possibly causing accelerated damage to the nozzles in a relatively short amount of time. In addition, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NOX). Conversely, a lower combustion gas temperature associated with reduced fuel flow and/or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons.
In a particular combustor design, the combustor may include an end cap that extends radially across at least a portion of the combustor. A plurality of tubes may be radially arranged in one or more tube bundles across the end cap to provide fluid communication for the compressed working fluid through the end cap and into a combustion chamber. Fuel supplied to a fuel plenum inside the end cap may flow around the tubes and provide convective cooling to the tubes before flowing across a baffle and into the tubes. The fuel and compressed working fluid mix inside the tubes before flowing out of the tubes and into the combustion chamber.
Although effective at enabling higher operating temperatures while protecting against flame holding and controlling undesirable emissions, the fuel flowing around and into the tubes may become unevenly heated, resulting in variations in the density and therefore the flow rate of fuel flowing into each tube. In addition, the temperature of the fuel may be significantly lower than the temperature of the compressed working fluid flowing around the end cap and through the tubes, creating undesirable thermal stresses across the end cap, baffle, and/or tubes that may reduce the low cycle fatigue limits of the combustor. As a result, a combustor and method for distributing fuel in the combustor that addresses one or more of these deficiencies would be useful.